Teeth for Interfaces

 A different kind of interaction.

Finally, Apps to Sink Your Teeth Into

By Paul Marks, Commissioned by CACM Staff,  January 12, 2021

Engineers exploring human-computer interaction have found yet another part of the body for our electronic devices to exploit: our teeth.

There is scarcely a part of the human body that has not been harnessed in some fashion to help control computing devices or to authenticate users.

Brain-computer interfaces, for instance, tap our thoughts for both machine and game control, while gaze-trackers capture our eyeball motion to sense what's grabbing our attention, and face and fingerprint recognition systems help confirm our identities.

Now, engineers exploring the field of human-computer interaction (HCI) have found yet another part of the body for our electronic devices to exploit: our teeth.

This might sound a peculiar choice, but this is not the work of one outlier research team. At three virtual conferences in September, three separate research teams revealed early versions of tooth-based technologies. These three systems, respectively, allow users to:

Control apps in a contactless, hands-free manner by tapping their teeth together to issue software commands;

Authenticate their identity by smiling and showing their unique tooth profile to their phone camera, and

Check their oral health with an app-connected dental device.

The first idea, called EarSense, was presented at September's ACM SIGMOBILE Mobicom 2020 event by  Jay Prakash of the University of Illinois at Urbana-Champaign. The technology Prakash and his team have developed re-engineers a smartphone's earpiece so it can work as a microphone as well as a loudspeaker, allowing it to detect when people tap their teeth together a number of times, or gently slide their teeth over each other.

Because the sound of tooth clicks and sliding sequences reverberate through the skull and jawbone (or mandible) up to the ear drum (in an acoustic phenomenon called cranio-mandibular transmission), the sounds can activate commands in, say, music and audiobook apps, perhaps clicking teeth twice for playback, three times to skip a track, and a slide of the teeth indicating playback should rewind a set number of seconds.

To make a tiny earpiece loudspeaker operate as a microphone, Prakash had to undertake a bit of software surgery on the diminutive soundcard inside the earpiece. "Typically, soundcards support toggling to operate in microphone or speaker mode, and this method of to-and-fro conversion is known as jack-retasking," he says. "We exploited this feature in Realtek soundcards to convert an earphone into an input transducer. By default, the system acts as a microphone and the moment there is a request to play music or make a call, it turns to speaker mode."  ... '